In recent years, IEEE 802.11 wireless local area networks (WLANs) have been rapidly deployed in enterprises, public areas and homes. Recent studies on operational WLANs have shown that user load is often distributed unevenly among wireless access points (APs). In current WLANs, each user scans the wireless channel in order to detect its nearby access points and then to associate itself with the access point that has the strongest received signal strength indicator (RSSI), while ignoring the load on the access point. As users are typically not uniformly distributed, most of them may be associated with just a few access points in a network, while adjacent or nearby access points may carry a light load or even be idle. This load imbalance among access points is undesirable because it hampers the network from providing satisfactory service to its users. Studies show that the problem can be alleviated by balancing the load among the access points.
Vendors of WLAN products have incorporated load balancing features in their network device drivers, access point firmware, and WLAN cards. In some of these proprietary solutions, the access points broadcast their load to users in their vicinity in the beacon messages thereby allowing each user to choose the least loaded access point. In other proposed techniques, rather than using the RSSI as the association criteria, the rules define different metrics and associate each user with the access point that optimizes these metrics. These metrics typically take into account factors such as the number of users currently associated with an access point, the mean RSSI of users currently associated with an access point, the RSSI of the new user, and the bandwidth a new user can obtain if it is associated with a particular access point. For example, new users are associated with the access point that can provide a minimal bandwidth required by the user. If there are multiple such access points available to a user, then the access point with the strongest signal is selected. Most of these techniques only determine the association of newly arrived users without redistributing or reassociating existing users on that access point. But one known technique proposes reassociation of users periodically each time some bandwidth thresholds are violated.
Load balancing has also been considered in cellular networks, both TDMA and CDMA networks. Usually, it is achieved via dynamic channel allocation techniques. These methods are not applicable in the WLAN environment where each access point normally uses one channel and channel allocation is fixed. These methods are also not applicable to CDMA packet data networks. Another approach for load balancing is to use cell overlapping to reduce the blocking probability of calls and maximize the network utilization. For example, a newly arrived mobile station is associated with the base station with the greatest number of available channels. Fairness in this type of approach has been addressed by restricting the number of available channels for new calls that are made in overlapping areas. It has also been proposed that the channel conditions of mobile stations associated with a base station be considered. Load balancing integrated with coordinated scheduling technique has been studied for CDMA networks.
Although many techniques exist for balancing loads in wireless networks, none of the known techniques provide a suitably fair technique for load balancing and none provide a guarantee on the bandwidth allocated to each user. Fair load balancing with a concomitant bandwidth allocation guarantee is absent from all the known techniques.